Question: $ \left(\dfrac{16}{81}\right)^{-\frac{3}{2}}$
$= \left(\dfrac{81}{16}\right)^{\frac{3}{2}}$ $= \left(\left(\dfrac{81}{16}\right)^{\frac{1}{2}}\right)^{3}$ To simplify $\left(\dfrac{81}{16}\right)^{\frac{1}{2}}$ , figure out what goes in the blank: $\left(? \right)^{2}=\dfrac{81}{16}$ To simplify $\left(\dfrac{81}{16}\right)^{\frac{1}{2}}$ , figure out what goes in the blank: $\left({\dfrac{9}{4}}\right)^{2}=\dfrac{81}{16}$ so $ \left(\dfrac{81}{16}\right)^{\frac{1}{2}}=\dfrac{9}{4}$ So $\left(\dfrac{81}{16}\right)^{\frac{3}{2}}=\left(\left(\dfrac{81}{16}\right)^{\frac{1}{2}}\right)^{3}=\left(\dfrac{9}{4}\right)^{3}$ $= \left(\dfrac{9}{4}\right)\cdot\left(\dfrac{9}{4}\right)\cdot \left(\dfrac{9}{4}\right)$ $= \dfrac{81}{16}\cdot\left(\dfrac{9}{4}\right)$ $= \dfrac{729}{64}$